CAIE
Chemistry
(9701)
Questions & Answers
Hydrogen peroxide, H , reacts rapidly with acidified potassium manganate(VII), KMnO
+ 2MnO
+ 8H O
+ 2Mn
You will determine the concentration of a solution of hydrogen peroxide. You will first dilute the solution and then carry out a titration with acidified potassium manganate(VII). FA 1 is aqueous hydrogen peroxide, H FA 2 is 0.0300 mol dm potassium manganate(VII), KMnO FA 3 is 1.0 mol dm sulfuric acid, H
Method Dilution of FA 1 of FA 1 into the 250 cm volumetric flask. of solution. T itration pipette with distilled water and then with FA 4. of FA 4 into a conical flask. measuring cylinder to add 10 cm of FA 3 to the conical flask. The rough titre is = cm volume of FA 2 added in each accurate titration. Keep FA 1 for use in Questions 2 and 3. Keep FA 2 for use in Question 3. * 0000800000002 * Results
From your accurate titration results, calculate a suitable mean value to use in your calculations. Show clearly how you obtain the mean value. 25.0 cm of FA 4 required cm of FA 2.
Calculations
Give your answers to (c)(ii), (c)(iii) and (c)(iv) to an appropriate number of significant figures.
Calculate the amount, in mol, of manganate(VII) ions in the volume of FA 2 in
. amount of MnO = mol
Calculate the amount, in mol, of hydrogen peroxide in 25.0 cm of FA 4. amount of H = mol
Calculate the concentration, in mol dm , of hydrogen peroxide in FA 1. concentration of H in FA 1 = mol dm [1]III VII * 0000800000003 *
A student suggests that the experiment would be more accurate if a 10 cm pipette is used to measure FA 3 in place of the measuring cylinder. State whether the student' s suggestion is correct. Explain your answer . Include a calculation as part of your explanation. [2] [Total: 14] * 0000800000004 * BLANK PAGE * 0000800000005 *
You will now determine the concentration of a solution of hydrogen peroxide by a dif ferent method. Hydrogen peroxide decomposes slowly into water and oxygen at room temperature. This reaction is exothermic. When a catalyst is added, the decomposition is fast and there is a measurable temperature rise.
O(l) +
FA 1 is aqueous hydrogen peroxide, H FA 5 is manganese( IV) oxide, MnO
Method Experiment 1 beaker. measuring cylinder to add 25.0 cm of FA 1 to the cup. thermometer is fully covered. Record the temperature in the space for results. Experiment 2 beaker. measuring cylinder to add 40.0 cm of FA 1 to the second cup. Keep FA 5 for use in Question 3. Results [5]III V * 0000800000006 *
Calculations
Calculate the energy change, in J, in Experiment 2. energy change = J
Use the information given and your answer to (b)(i) to calculate the concentration, in mol dm , of hydrogen peroxide in FA 1. concentration of H in FA 1 = mol dm
The concentration of hydrogen peroxide in FA 1 calculated using the method given for Question 1 is more accurate than that using the method given for Question 2.
Heat loss is a large source of error when carrying out the method for Question 2. Describe and explain the ef fect of heat loss on the value of the concentration of hydrogen peroxide calculated.
A student suggests that calculating the concentration of hydrogen perox ide using the method in Question 2 would be less accurate when the concentration is lower. Suggest whether the student is correct. Explain your answer. [Total: 10] * 0000800000007 * Qualitative analysis For each test you should record all your observations in the spaces provided. Examples of observations include: added You should record clearly at what stage in a test an observation is made. Where no change is observed, you should write 'no change'. Where reagents are selected for use in a test, the name or correct formula of the element or compound must be given. If any solution is warmed, a boiling tube must be used. If a solid is heated, a hard-glass test-tube must be used. Rinse and reuse test-tubes and boiling tubes where possible. No additional tests should be attempted.
(i) Transfer a 2 cm depth of FA 2, KMnO , into a test-tube. Add the same volume of aqueous sodium hydroxide followed by a small spatula measure of FA 5, MnO . Stir for approximately 30 seconds then filter the mixture into a second test-tube. observations Add dilute sulfuric acid to the filtrate until no further change. observations
Transfer a 1 cm depth of aqueous iron(II) sulfate into a boiling tube. Add the same depth of dilute sulfuric acid followed by a very small spatula measure of FA 5, MnO . Carefully warm the mixture using a Bunsen burner for about 20 seconds. Filter the warm mixture into a test-tube. observations Add aqueous sodium hydroxide dropwise to the filtrate until no further change. observations [2] * 0000800000008 *
Suggest a conclusion about the chemical behaviour of FA 5 using your observations in
(ii). FA 5 is acting as
Write an ionic equation for the reaction between aqueous sodium hydroxide and the filtrate in (a)(ii). Include state symbols. Question 3 continues on page 10. * 0000800000009 *
FA 6 and FA 7 are both aqueous solutions of salts. Neither solution includes an ion that contains sulfur. FA 6 contains two cations and one anion. Two of the ions are listed in the Qualitative analysis notes. FA 7 contains one cation and one anion. One of the ions is listed in the Qualitative analysis notes.
Carry out the following tests and record your observations in Table 3.1. Use a 1 cm depth of FA 6 or FA 7 in a boiling tube for Test 1. Use a 1 cm depth of FA 6 or FA 7 in a test-tube for Tests 2, 3 and 4. Table 3.1 test observations FA 6 FA 7 Test 1 Add aqueous sodium hydroxide, then warm gently. Test 2 Add acidified aqueous KMnO dropwise until no further change. Test 3 Add an equal volume of FA 1, then add a few drops of starch solution. Test 4 Add aqueous sodium carbonate. [6] * 0000800000010 *
The anion in FA 6 does not contain nitrogen. Select one further reagent to identify the anion present in FA 6. Carry out a test with this reagent and record your observations in Table 3.2. Table 3.2 reagent observations
Give the formulae of the ions present in FA 6 and FA 7. If you are unable to identify an ion from your tests, write 'unknown.' The ions present in FA 6 are and and . The ions present in FA 7 are and . [3] [Total: 16] * 0000800000011 * BLANK PAGE * 0000800000012 * BLANK PAGE * 0000800000013 * Qualitative analysis notes 1 Reactions of cations cation reaction with NaOH(aq) NH
aluminium, Al
white ppt. soluble in excess white ppt. insoluble in excess ammonium, NH
no ppt. ammonia produced on warming barium, Ba
faint white ppt. is observed unless [Ba
] is very low no ppt. calcium, Ca
white ppt. unless [Ca
] is verylow no ppt. chromium(III), Cr
grey-green ppt. soluble in excess giving dark green solution grey-green ppt. insoluble in excess copper(II), Cu
pale blue ppt. insoluble in excesspale blue ppt. soluble in excess giving dark blue solution iron(II), Fe
green ppt. turning brown on contact with air insoluble in excess green ppt. turning brown on contact with air insoluble in excess iron(III), Fe
red-brown ppt. insoluble in excessred-brown ppt. insoluble in excess magnesium, Mg
white ppt. insoluble in excesswhite ppt. insoluble in excess manganese(II),
off-white ppt. rapidly turning brown on contact with air insoluble in excess off-white ppt. rapidly turning brown on contact with air insoluble in excess zinc, Zn
white ppt. soluble in excess white ppt. soluble in excess 2 Reactions of anions anion reaction carbonate, CO liberated by dilute acids chloride, Cl
gives white ppt. with Ag
(soluble in NH
) bromide, Br
gives cream / off-white ppt. with Ag
(partially soluble in NH
) iodide, I
gives pale yellow ppt. with Ag
(insoluble in NH
) nitrate, NO
NH liberated on heating with OH
and Al foil nitrite, NO
NH liberated on heating with OH
and Al foil; decolourises acidified aqueous KMnO sulfate, SO
gives white ppt. with Ba
(insoluble in excess dilute strong acids); gives white ppt. with high [Ca
] sulfite, SO
gives white ppt. with Ba
(soluble in excess dilute strong acids); decolourises acidified aqueous KMnO thiosulfate, S
gives off-white / pale yellow ppt. slowly with H + * 0000800000014 * 3 Tests for gases gas test and test result ammonia, NH turns damp red litmus paper blue carbon dioxide, CO gives a white ppt. with limewater hydrogen, H 'pops' with a lighted splint oxygen, O relights a glowing splint
Tests for elements element test and test result iodine, I gives blue-black colour on addition of starch solution Important values, constants and standards molar gas constant R = 8.31 J Kmol Faraday constant F = 9.65 × 10 C mol Avogadro constant L = 6.02 × 10mol electronic charge e = -1.60 × 10-19 molar volume of gas V = 22.4 dmmol at s.t.p. (101 kPa and 273 K) = 24.0 dmmol at room conditions ionic product of water K = 1.00 × 10-14mol (at 298 K (25 °C)) specific heat capacity of waterc = 4.18 kJ kg (4.18 J g ) * 0000800000015 * Group The Periodic Ta ble of Elements hydrogen 1.0 helium 4.0 12 13 14 15 16 17 18 3456789 10 11 12 lithium 6.9 beryllium 9.0 atomic number atomic symbolKey name relative atomic mass sodium 23.0 magnesium 24.3 potassium 39.1 calcium 40.1 rubidium 85.5 strontium 87.6 caesium 132.9 barium 137.3 francium radium boron 10.8 aluminium 27.0 gallium 69.7 indium 114.8 thallium 204.4 carbon 12.0 silicon 28.1 germanium 72.6tin 118.7 lead 207.2 titanium 47.9 zirconium 91.2 hafnium 178.5 rutherfordium vanadium 50.9 niobium 92.9 tantalum 180.9 dubnium chromium 52.0 molybdenum 95.9 tungsten 183.8 seaborgium manganese 54.9 technetium rhenium 186.2 bohrium iron 55.8 ruthenium 101.1 osmium 190.2 hassium cobalt 58.9 rhodium 102.9 iridium 192.2 meitnerium nickel 58.7 palladium 106.4 platinum 195.1 darmstadtium copper 63.5 silver 107.9 gold 197.0 roentgenium zinc 65.4 cadmium 112.4 mercury 200.6 copernicium flerovium livermorium nitrogen 14.0 phosphorus 31.0 arsenic 74.9 antimony 121.8 bismuth 209.0 oxygen 16.0 sulfur 32.1 selenium 79.0 tellurium 127.6 polonium fluorine 19.0 chlorine 35.5 bromine 79.9 iodine 126.9 neon 20.2 argon 39.9 krypton 83.8 xenon 131.3 radon nihonium moscovium tennessine oganesson scandium 45.0 yttrium 88.9 57-71 lanthanoids 89-103 actinoids lanthanum 138.9 lanthanoids actinoids actinium cerium 140.1 thorium 232.0 praseodymium 140.9 protactinium 231.0 neodymium 144.2 uranium 238.0 promethium neptunium samarium 150.4 plutonium europium 152.0 americium gadolinium 157.3 curium terbium 158.9 berkelium dysprosium 162.5 californium holmium 164.9 einsteinium erbium 167.3 fermium thulium 168.9 mendelevium ytterbium 173.1 nobelium lutetium 175.0 lawrencium To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cambridgeinternational.org after the live examination series. * 0000800000016 *